This invention relates to a novel nematic liquid crystal compound of an ethane derivative useful as an electro-optical material, and a liquid crystal composition containing the same.
Display elements utilizing liquid crystals have been broadly used for watches, electric calculators, etc. These liquid crystal display elements utilize the optical anisotropy and dielectric anisotropy of liquid crystal substances, and the liquid crystal phases include nematic phase, smectic phase and cholesteric phase. However, among these display elements, those utilizing nematic liquid crystals have been most broadly practically used. They are classified into TN (twisted nematic) type, DS (dynamic scattering) type, guest-host type, DAP type, etc., and various characteristics are required for liquid crystal substances used for these respective display elements. Among the characteristics, however, an important one required for various display cells in common thereto is that a nematic phase is exhibited within a broad temperature range including room temperature. Most of practically usable materials having such a characteristic have usually been prepared by blending several kinds or more of components consisting of compounds having nematic phase in the vicinity of room temperature and compounds having nematic phase within a temperature region higher than room temperature. Most of liquid crystalline blends prepared as above and currently practically used have been required to have nematic phase over the whole temperature range of at least from -30.degree. C. to +65.degree. C. In order to satisfy such a requirement, the following compounds have often been used as the compounds having nematic phase within a temperature range higher than room temperature:
compounds having a crystalline phase-nematic phase transition point (C-N point) of about 100.degree. C. and also having a nematic phase-isotropic liquid transition point (N-I point) of about 200.degree. C., such as 4,4'-substituted-terphenyl, 4,4'-substituted-biphenylcyclohexane, 4,4'-substituted-benzoyloxybenzoic acid phenyl ester, etc.
These compounds, however, have undesirable properties of raising the viscosity of the resulting liquid crystalline blends to thereby retard the response rate.